Richardson Number | Ellrod Index | Interval Values of Ellrod Index | Turbulence CAPE Index

Atmospheric Turbulence

Richardson Number

The Richardson number is the ratio of buoyancy and flow shear terms. It is expressed by a dimensionless number between 0 and 10. In aviation the Richardson Number can be used to assess atmospheric turbulence. This is also referred to as Clear Air Turbulence (CAT). Values below unity indicate significant turbulence.


Available levels: 100hPa, 300hPa, 500hPa


Ellrod Index

The Ellrod Index is designed to detect regions of Clear-Air-Turbulence (CAT) in the atmosphere. It is computed based on horizontal deformation of air parcels and vertical wind shear. The unit is s-2.

  • Especially suitable to detect turbulence near the jet stream; at upper level troughs and ridges, and the exit region of a jet
  • Does NOT account for low level turbulence due to thunderstorms, mountain ranges, etc.
0-2smooth conditions
2-9light turbulence
9-20moderate turbulence
20-36severe turbulence
> 36extreme turbulence

Available levels (global): 950hPa, 925hPa, 900hPa, 850hPa, 800hPa, 700hPa, 500hPa, 300hPa, 250hPa, 200hPa, 150hPa, 100hPa, 70hPa, 50hPa, 10hPa
Available flight levels (global): FL20 - FL900 (continuously)


Interval Values of Ellrod Index

Gives the mean, maximum or minimum ellrod index at the indicated flight level over the indicated duration.


Available flight levels: FL20 - FL900 (continuously)

Available measures: mean, min, max

Available intervals: 1h, 3h, 6h, 12h, 24h


Turbulence CAPE Index

Turbulence index incorporating CAPE. The index is computed for the total atmospheric column and not for single layers. This index allows for checking if turbulence is present. The values range from 0 (no turbulence expected) to 1 (turbulence expected)